Particle deposition system with enhanced speed and diameter accuracy

ABSTRACT

In a method for depositing particles onto a substrate a flow of gas containing particles is provided along a flow path that bypasses a deposition chamber. The flow path may direct the flow of the gas containing the particles to a vacuum. To deposit particles onto a substrate in the deposition chamber, the flow path of the gas containing the particles is diverted into the deposition chamber so that particles are deposited onto the substrate. After a desired amount of particles have been deposited onto the substrate, the flow path of the flow of the gas containing the particles is changed to the flow path that bypasses the deposition chamber. A particle deposition system and a method for maintaining particle diameter during deposition of particles onto a substrate also are described.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No.10/074,354, filed Feb. 11, 2002, which claims priority under 35 U.S.C. §119(e) from U.S. Provisional Patent Application No. 60/267,613, filedFeb. 9, 2001. The disclosures of these prior applications areincorporated herein by reference.

BACKGROUND OF THE INVENTION

The present invention relates generally to particle deposition and, moreparticularly, to a system and methods for efficiently depositing smallparticles on substrates.

Particle scanners are used to detect contamination on the surfaces ofsemiconductor wafers, computer disks, flat panel display glass, andother industrial substrates that may be sensitive to contamination. Ingeneral, these scanners operate by sensing light scattered by particlesas a laser is scanned over the substrate surface. To calibrate thesescanners, particles of a known size and known diameter distribution areused. The particles typically used in scanner calibration arepolystyrene latex (PSL) spheres. To create a sample for use in scannercalibration, a particle deposition system is used to deposit a knownamount of PSL spheres having a known particle size and a known diameterdistribution onto the surface of the sample. During the depositionprocess, it is important that the particle deposition system does notintroduce other contamination onto the sample surface.

Known particle deposition systems typically atomize a suspension ofparticles, e.g., PSL spheres, in clean water (or other fluid) to form aspray in a flow of clean air. After the particles dry, they are eitherled directly to the sample or may pass through any of several devices tocontrol or monitor flow rates and electrically charge or discharge theparticles. One common technique is to pass the particle flow through adifferential mobility analyzer (DMA), which passes only a selected bandof charged particle diameters through a narrow slit in a rod. Anelectric field draws the charged particles sideways through the clean,laminar airflow toward the rod. The smaller particles are drawn throughthe airflow more easily and therefore reach the rod before largerparticles. By adjusting the electric field, the particle diameter thatpasses the slit can be selected. Control of the particle diameterselection process depends on the temperature and flow parameters in thesystem as well as the voltage controlling the electric field.

It has recently become more important to control precisely the particlediameter selection process to satisfy the semiconductor industry's needfor more precise information regarding the true size of the particlesbeing deposited. Commercially available particle deposition systems donot adequately monitor all of the parameters needed to obtain long-termcontrol of the DMA. Consequently, these systems suffer from an unwantedvariation in the relationship between the particle diameter passing theslit and the applied control voltage.

U.S. Pat. No. 5,534,309 to Liu discloses a method and apparatus fordepositing particles on a semiconductor wafer. The disclosed methodrequires that a purging step be conducted to remove unwanted particlesfrom the deposition chamber before the wafer is placed in the chamber.Another purging step is conducted at the end of each deposition beforethe wafer is removed from the chamber. These purging steps require thatthe wafer be removed from the deposition chamber at the end of eachdeposition. Thus, the production of sample wafers having multiple spotdepositions thereon requires that the wafers must be moved into and outof the deposition chamber repeatedly. This frequent handling of thewafers significantly slows the production of sample wafers havingmultiple spot depositions. In addition, it also may introduce the wafersto contamination, which is undesirable in clean room operations.

In view of the foregoing, there is a need for a particle depositionsystem that enables the size of the particles being deposited to beprecisely controlled and that reduces the time required to producestandards, e.g., sample wafers for use in scanner calibration.

SUMMARY OF THE INVENTION

Broadly speaking, the present invention fills this need by providing aparticle deposition system that controls the flow of gas containingparticles into a deposition chamber so that unwanted particles do notenter the deposition chamber. The particle deposition system alsomonitors the flow of the gas containing the particles so that thedeposited particle diameter remains substantially constant during thedeposition process.

In accordance with one aspect of the invention, a method for depositingparticles onto a substrate is provided. In this method, a flow of gascontaining particles is provided along a flow path that bypasses adeposition chamber. To deposit particles onto a substrate in thedeposition chamber, the flow path of the gas containing the particles ischanged so that the flow of the gas containing the particles causesparticles to be deposited onto the substrate. After a desired amount ofparticles have been deposited onto the substrate, the flow path of theflow of the gas containing the particles is changed to the flow paththat bypasses the deposition chamber.

In one embodiment, the flow of the gas containing the particles flowsinto a vacuum that is coupled in flow communication with the depositionchamber. In this embodiment, the vacuum is configured to prevent theflow of the gas containing the particles from entering the depositionchamber without drawing any significant amount of air from thedeposition chamber. In one embodiment, the flow of the gas containingthe particles is diverted from the vacuum to the deposition chamber byinterrupting the flow communication between the vacuum and the flow ofthe gas containing the particles.

In another embodiment, particles are deposited onto the substrate inaccordance with a first set of deposition parameters. Thereafter,without removing the substrate from the deposition chamber, particlesare deposited onto the substrate using a second set of depositionparameters. In one embodiment, particles having the same particle sizeare deposited in different spot locations on the substrate. In anotherembodiment, particles having different particle sizes are deposited indifferent spot locations on the substrate.

In accordance with another aspect of the invention, a method formaintaining particle diameter during deposition of particles onto asubstrate is provided. In this method, gases are flowed into adifferential mobility analyzer (DMA) having a slit for passing particlestherethrough. At least one of the gases flowed into the DMA containsparticles. The gases flowing into and out of the DMA are monitored, andperiodic adjustments are made to the voltage applied to the DMA so thata particle size diameter passed through the slit remains substantiallyconstant during the deposition process. In one embodiment, themonitoring of the flows into and out of the DMA includes measuring thepressure differential across orifices located before and after the DMA.

In accordance with yet another aspect of the invention, a particledeposition system is provided. In one embodiment, the particledeposition system includes a deposition chamber having an inlet and aconduit coupled to this inlet. The conduit, which has a first branch anda second branch, is in flow communication with a source of gascontaining particles. A particle counter is disposed in the first branchof the conduit and an orifice is disposed in the second branch of theconduit. A vacuum is coupled in flow communication with the first andsecond branches of the conduit.

In another embodiment, the particle deposition system includes anatomizer for providing a flow of gas containing particles. A flowcontrol device is coupled in flow communication with the atomizer, and adifferential mobility analyzer (DMA) is coupled in flow communicationwith the flow control device. A deposition chamber is coupled in flowcommunication with the flow control device and the DMA. When theparticles in the flow of the gas containing the particles are to befiltered by the DMA, the flow control device directs the flow of the gascontaining the particles toward the DMA. When the particles in the flowof the gas containing the particles are not to be filtered by the DMA,the flow control device directs the flow of the gas containing theparticles toward the deposition chamber.

The present invention advantageously enables particles having a constantparticle diameter to be deposited onto a substrate in a depositionchamber without introducing unwanted particles in the depositionchamber. This avoids the need to purge the deposition chamber betweendepositions. Consequently, multiple depositions can be made on asubstrate without removing the substrate from the deposition chamber. Byminimizing the handling of the substrate required for deposition, thepresent invention significantly decreases the time required to producestandards having multiple depositions thereon. It also minimizes theopportunity for contamination to be introduced onto the substrate duringthe deposition process.

It is to be understood that the foregoing general description and thefollowing detailed description are exemplary and explanatory only andare not restrictive of the invention, as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute partof this specification, illustrate exemplary embodiments of the inventionand together with the description serve to explain the principles of theinvention.

FIG. 1 is a simplified schematic diagram of an exemplary particledeposition system in accordance with one embodiment of the presentinvention.

FIG. 2 is a block diagram that illustrates how a computer can be used tocontrol the operation of the exemplary particle deposition system shownin FIG. 1 using real time feedback.

FIG. 3 is a flow chart diagram that illustrates the method operationsperformed in depositing particles onto a substrate in accordance withone embodiment of the present invention.

FIG. 4 is a flow chart diagram that illustrates the method operationsperformed in depositing particles onto a substrate in accordance withanother embodiment of the present invention.

FIG. 5 is a flow chart diagram that illustrates the method operationsperformed in maintaining particle diameter during deposition ofparticles in accordance with one embodiment of the present invention.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Several exemplary embodiments of the invention will now be described indetail with reference to the accompanying drawings.

FIG. 1 is a simplified schematic diagram of an exemplary particledeposition system in accordance with one embodiment of the presentinvention. As shown in FIG. 1, particle deposition system 100 is coupledin flow communication with gas source 102 via pressure valve 104. By wayof example, gas source 102 may be a source of nitrogen or compressed dryair (CDA). When pressure valve 104 is open, gas from gas source 102flows into conduit system 106. Pressure gauge 108, which is disposedjust after pressure valve 104, monitors the gas pressure in conduitsystem 106. Conduit system 106 includes a branch T1 that directs the gasflow along flow paths 106 a and 106 b. Flow path 106 a directs the gasflow toward atomizer flow controller 110 and flow path 106 b directs thegas flow toward makeup flow controller 112. Conduit system 106 includesanother branch T2 that directs a portion of the gas flow from flow path106 a along flow path 106 c, which directs the gas flow toward sheathflow controller 114.

The gas flow passing by branches T1 and T2 along flow path 106 a entersatomizer flow controller 110, which may be any suitable flow controllerthat can be controlled to allow the gas to flow therethrough at adesired rate. In one embodiment, the gas flow through atomizer flowcontroller 110 is in the range from about 5 liters/minute to 6liters/minute. The gas flows from atomizer flow controller 110 intoatomizer 118, which includes orifice 118 a. The size of orifice 118 a isselected to allow a desired amount of gas to flow therethrough. As iswell known to those skilled in the art, atomizer 118, which includes abowl containing deionized water (DIW) and particles, introduces wetparticles into the gas flow and thereby generates an aerosol flow. Whenparticle deposition system 100 is being used to make standards, theparticles provided in atomizer 118 are typically polystyrene latex (PSL)particles having a uniform shape and a uniform particle size. It will beapparent to those skilled in the art that particle deposition system 100also may be used to deposit other man made particles as well asnaturally occurring particles that have nonuniform shapes and nonuniformparticle sizes. By way of example, the naturally occurring particles maybe particles of silicon, tungsten, copper, or aluminum oxide.

The aerosol flow leaving atomizer 118 flows through water trap 120,which is a safety device that captures any excess water that is drawninto conduit system 106. After passing through water trap 120, theaerosol flow flows into three-way solenoid 122, which can be controlledto direct the aerosol flow along either flow path 106 a or flow path 106d. In one embodiment, three-way solenoid 122 is controlled based on thesize of the particles in the aerosol flow as will be described in moredetail below. Those skilled in the art will recognize that othersuitable flow switching devices, e.g., valves, may be used in place ofthree-way solenoid 122.

When the three-way solenoid 122 directs the aerosol flow along flow path106 a, the aerosol flow flows into dryer 124, which performs twofunctions. First, dryer 124 dries the relatively small particles in theaerosol flow to ensure that such particles are not encapsulated in waterdroplets. If the particles are encapsulated in water droplets, then theymay behave like larger particles. This is undesirable because it mayprevent properly sized particles from being passed through adifferential mobility analyzer (DMA), as described later. Second, dryer124 exhausts some of the aerosol flow to atmosphere via orifice 126 tominimize the flow into the DMA. The aerosol flow leaving dryer 124 flowsthrough orifice 128 and into ionizer 130. The size of orifice 128 isselected to allow a desired amount of gas to flow therethrough. Pressuresensors 132 a and 132 b are situated on opposing sides of orifice 128 sothat the pressure differential, ΔP, across this orifice can bedetermined. Using the pressure differential across orifice 128determined by pressure sensors 132 a and 132 b and the size of theorifice, a computer can calculate the aerosol flow through the orifice.Ionizer 130 changes the charge distribution of the particles in theaerosol flow before the aerosol flow reaches DMA 134, which passesmostly singly charged particles having a certain size. The use ofionizer 130 is necessary because the particles in the aerosol flow arehighly charged when they leave atomizer 118. As is well known to thoseskilled in the art, ionizer 130 includes a radioactive source thatintroduces charged ions into the aerosol flow. The aerosol flow leavingionizer 130 includes a reasonable fraction of singly charged particlesthat can be handled by DMA 134.

The aerosol flow leaving ionizer 130 flows into DMA 134. A flow of cleansheath gas also flows into DMA 134 along flow path 106 c. Sheath flowcontroller 114, which may be any suitable flow controller, controls theflow rate of the clean sheath gas into DMA 134. DMA 134 may be anysuitable commercially available DMA and those skilled in the art arefamiliar with the structure and operation of such DMAs. In short, DMA134 includes an outer tube and an inner rod, which has a slit toward thebottom thereof (neither the outer tube nor the inner rod is shown inFIG. 1). A negative voltage is applied to the inner rod and,consequently, positively charged particles are attracted toward theinner rod. On the other hand, negatively charged particles are repelledtoward the outer tube. At the same time, the laminar flow of cleansheath gas moves the particles through DMA 134, i.e., from the top ofthe DMA to the bottom of the DMA. The smaller, positively chargedparticles are attracted to the inner rod while the larger particles areimpacted out. As is well known to those skilled in the art, onlyparticles having the diameter of interest will pass through the slit.The aerosol flow containing particles that have passed through the slitexits the bottom of DMA 134 and flows toward orifice 136.

The excess gas flow exits the bottom of DMA 134 and any excess particlesin the excess gas flow are captured in filter 138 so that they can bedisposed of as waste. The excess gas flow flows from filter 138 intoexcess flow controller 140 and is then discharged to the atmosphere.Excess flow controller 140 may be any suitable flow controller that cancontrol the flow rate of the excess gas flow out of DMA 134. In oneembodiment, excess flow controller 140 controls the flow rate of theexcess gas flow so that this flow rate matches the flow rate of thesheath gas flowing into DMA 134 along flow path 106 c.

As noted above, the aerosol flow containing particles that have passedthrough the slit, i.e., the sized particles that will be used in thedeposition, exits the bottom of DMA 134 and flows into orifice 136. Thesize of orifice 136 is selected to allow a desired amount of gas to flowtherethrough. Pressure sensors 132 a and 132 b are situated on opposingsides of orifice 136 so that the pressure differential, ΔP, across thisorifice can be determined. Using the pressure differential acrossorifice 136 determined by pressure sensors 132 a and 132 b and the sizeof the orifice, a computer can calculate the aerosol flow through theorifice. After passing through orifice 136, the aerosol flow continuesto flow along flow path 106 a toward deposition chamber 138. Once theaerosol flow flows by branch T3, branch T4 directs the aerosol flowtoward deposition chamber 138. Branch T4 also directs the gas flowflowing along flow path 106 b toward deposition chamber 138. Makeup flowcontroller 112, which may be any suitable flow controller, controls theflow rate of the gas flow along flow path 106 b. In one embodiment,makeup flow controller 112 controls the flow rate of the gas flow alongflow path 106 b so that the combination of this flow rate and the flowrate of the aerosol flow exiting DMA 134 slightly exceeds the flow ratethat is removed from the aerosol gas flow for purposes of particlecounting, as will be explained in more detail later.

The combined aerosol flow, which includes the aerosol flow from flowpath 106 a and the gas flow from flow path 106 b, flows from branch T4toward deposition chamber 138. When a deposition is in progress, avacuum causes branch T5 to direct a portion of the combined aerosol flowtoward condensation nucleus counter (CNC) 140 along vacuum flow path 106e. CNC 140 may be any suitable commercially available CNC. It will beapparent to those skilled in the art that other suitable particlecounters also may be used. As is well known to those skilled in the art,CNC 140 counts the particles in the combined aerosol flow and therebyenables a deposition process to be stopped when a desired particle counthas been reached. After passing through CNC 140, the combined aerosolgas flow flows through orifice 142 and two-way solenoid 144 a, which iscoupled in flow communication with vacuum system 146. Two-way solenoid144 a functions as on/off switch for vacuum system 146. Those skilled inthe art will recognize that other suitable flow switching devices, e.g.,valves, may be used in place of two-way solenoid 144 a (as well astwo-way solenoids 144 b and 144 c described below). When a deposition isin progress, two-way solenoid 144 a is open so that the vacuum draws aportion of the combined aerosol flow into vacuum flow path 106 e. In oneembodiment, the flow rate of the combined aerosol flow through CNC 140is substantially constant because orifice 142 is run at criticalpressure.

The remaining portion of the combined aerosol flow, i.e., the portionthat is not drawn into vacuum flow path 106 e, flows into depositionchamber 138 via aerosol inlet 138 a. By way of example, in oneembodiment, the aerosol flow exiting DMA 134 has a flow rate of about0.5 liter/minute and makeup flow controller 112 controls the gas flowrate in flow path 106 b such that this flow rate is about 2.4liters/minute. Thus, the flow rate of the combined aerosol flow is about2.9 liters/minute. In this embodiment, CNC 140 removes about 2.8liters/minute from the combined aerosol flow for purposes of particlecounting. Consequently, the remaining portion of the combined aerosolflow that flows into deposition chamber 138 has a flow rate of about 0.1liter/minute. It is to be understood that the flow into the depositionchamber may have a flow rate higher than 0.1 liter/minute, but such aflow rate is less preferred because it may cause the particles to spreadout beyond the desired spot diameter.

The particles in the aerosol flow entering deposition chamber 138 aredeposited onto substrate 10, which is supported on support member 12. Byway of example, substrate 10 may be a semiconductor wafer. Supportmember 12 may be any suitable support member, but preferably is asupport member that is capable of moving substrate 10 within depositionchamber 138. In one embodiment, support member 12 is capable of movingsubstrate 10 in a linear fashion as well as a rotary fashion. For aso-called full deposition, i.e., a deposition on the full surface ofsubstrate 10, the substrate is typically disposed 3 to 4 inches belowaerosol inlet 138 a. For a so-called spot deposition, i.e., a depositionon a small portion of substrate 10, a nozzle (not shown in FIG. 1) isdisposed in deposition chamber 138 in flow communication with aerosolinlet 138 a and the substrate is typically disposed about 0.25 inchbelow the outlet of the nozzle.

When DMA 134 is being used to size the particles, the deposition processis stopped using a vacuum that causes branch T7 to direct the remainingportion of the combined aerosol flow along vacuum flow path 106 g. Thevacuum is controlled by two-way solenoid 144 c, which is coupled in flowcommunication with vacuum system 146 and functions as on/off switch forthe vacuum system. Orifice 148 is situated between branch T7 and two-waysolenoid 144 c. In one embodiment, the size of orifice 148 is selectedso that the flow rate through this orifice slightly exceeds the flowrate of the remaining portion of the combined aerosol flow intodeposition chamber 138. Thus, when two-way solenoid 144 c is open, thevacuum draws the entirety of the remaining portion of the combinedaerosol flow into vacuum flow path 106 g. Consequently, none of thisflow enters deposition chamber 138.

The foregoing description describes the gas flow through particledeposition system 100 when the system is being run in DMA mode, i.e.,when DMA 134 is being used to size the particles that will enterdeposition chamber 138. Particle deposition system 100 also may be runin bypass mode, however. Bypass mode enables particle deposition system100 to be used to deposit particles without passing the particlesthrough the DMA. By way of example, bypass mode may be used to depositrelatively large particles that cannot be sized by DMA 134. In oneexemplary embodiment, particle deposition system 100 is run in DMA modewhen the aerosol flow includes relatively small particles, e.g.,particles having a particle size up to 1.5 microns, and the particledeposition system is run in bypass mode when the aerosol flow includesrelatively large particles, e.g., particles having a particle sizelarger than 1.5 microns. It will be apparent to those skilled in the artthat the particle deposition system can be run in DMA mode usingparticles larger than 1.5 microns when the DMA is capable of filteringsuch larger particles. To switch particle deposition system 100 intobypass mode, three-way solenoid 122 is activated to direct the aerosolflow along flow path 106 d. Branch T3 directs the aerosol flow towardbranch T4, which in turn directs the aerosol flow toward depositionchamber 138. Branch T4 also directs the gas flow flowing along flow path106 b toward deposition chamber 138. In one embodiment, makeup flowcontroller 112 controls the flow rate of the gas flow along flow path106 b so that the combination of this flow rate and the flow rate of theaerosol flow from flow path 106 d slightly exceeds the flow rate that isremoved from the aerosol gas flow by CNC 140, as described above.

The combined aerosol flow, which includes the aerosol flow from flowpath 106 d and the gas flow from flow path 106 b, flows from branch T4toward deposition chamber 138. As described above, when a deposition isin progress, a vacuum causes branch T5 to direct a portion of thecombined aerosol flow toward CNC 140 along vacuum flow path 106 e. Theremaining portion of the combined aerosol flow, i.e., the portion thatis not drawn into vacuum flow path 106 e, flows into deposition chamber138 via aerosol inlet 138 a. In bypass mode, the deposition process isstopped using a vacuum that causes branch T6 to direct the remainingportion of the combined aerosol flow along vacuum flow path 106 f. Thevacuum is controlled by two-way solenoid 144 b, which is coupled in flowcommunication with vacuum system 146 and functions as on/off switch forthe vacuum system. Orifice 150 is situated between branch T6 and two-waysolenoid 144 b. In one embodiment, the size of orifice 150 is selectedso that the flow rate through this orifice slightly exceeds the flowrate of the remaining portion of the combined aerosol flow intodeposition chamber 138. Thus, when two-way solenoid 144 b is open, thevacuum draws the entirety of the remaining portion of the combinedaerosol flow into vacuum flow path 106 f. Consequently, none of thisflow enters deposition chamber 138.

FIG. 2 is a block diagram that illustrates how a computer can be used tocontrol the operation of particle deposition system 100 shown in FIG. 1using real time feedback. As shown in FIG. 2, along flow path 106 a,computer 200 is coupled to atomizer flow controller 110, three-waysolenoid 122, dryer 124, the first pair of pressure sensors 132 a and132 b (located before DMA 134), DMA 134, excess flow controller 140, andthe second pair of pressure sensors (located after DMA 134). Along flowpath 106 b, computer 200 is coupled to makeup flow controller 112. Alongflow path 106 c, computer 200 is coupled to sheath flow controller 114.Along flow path 106 d, computer 200 is coupled to three-way solenoid122. Along vacuum flow path 106 e, computer 200 is coupled to CNC 140and two-way solenoid 144 a. Along vacuum flow path 106 f, computer 200is coupled to two-way solenoid 144 b. Finally, along vacuum flow path106 g, computer 200 is coupled to two-way solenoid 144 c.

Computer 200 sets and reads back the flows through atomizer flowcontroller 110, makeup flow controller 112, sheath flow controller 114,and excess flow controller 140. To control whether particle depositionsystem 100 operates in DMA mode or bypass mode, computer 200 sends acontrol signal to three-way solenoid 122 that causes this solenoid todirect the flow along the desired flow path, i.e., flow path 106 a orflow path 106 d. Computer 200 reads back the temperature within dryer124. To determine the particle input into DMA 134, computer 200 readsback the pressures detected by the first pair of pressure sensors 132 a,132 b, and determines the pressure differential, ΔP, across orifice 128(see FIG. 1). Using this pressure differential and the size of orifice128, computer 200 calculates the aerosol flow through orifice 128. Todetermine the particle flow out of DMA 134, computer 200 reads back thepressures detected by the second pair of pressure sensors 132 a, 132 b,and determines the pressure differential, ΔP, across orifice 136 (seeFIG. 1). Using this pressure differential and the size of orifice 136,computer 200 calculates the aerosol flow through orifice 136.

To control the size of the particle passed by DMA 134, computer 200controls the voltage applied to the inner rod of the DMA. The appliedvoltage required for DMA 134 to pass particles having a specific size isa function of the flows into and out of the DMA. Accordingly, computer200 periodically, e.g., every few seconds, uses an equation known tothose skilled in the art to calculate the voltage required for DMA 134to pass the desired particle size based on the current flows into andout of the DMA, i.e., the aerosol flow through orifice 128 before theDMA, the flow through sheath flow controller 114, the flow throughorifice 136 after the DMA, and the flow through excess flow controller140. Computer 200 then compares the calculated voltage with the voltagecurrently being applied to DMA 134 and, if necessary, adjusts thevoltage being applied to the DMA. By controlling the voltage applied toDMA 134 in this manner, computer 200 ensures that the passed particlesize remains constant during the deposition process.

Regarding particle counting, computer 200 sets the particle countingparameters used by CNC 140 and reads back the particle count from theCNC. Whenever the particle counter is put into operation, computer 200sends a control signal to two-way solenoid 144 a that opens thissolenoid and thereby puts vacuum system 146 (see FIG. 1) in flowcommunication with vacuum flow path 106 e. Computer 200 also sendscontrol signals to two-way solenoids 144 b and 144 c. When particledeposition system 100 is operating in DMA mode, two-way solenoid 144 bis closed so that vacuum flow path 106 f is not in flow communicationwith vacuum system 146. During the initial stabilization of particledeposition system 100 in DMA mode, computer 200 keeps two-way solenoid144 c open so that vacuum flow path 106 g is in flow communication withvacuum system 146. As described above, this causes the aerosol flow tobe drawn into the vacuum system via vacuum flow path 106 g. Wheneverparticles are to be deposited into deposition chamber 138 (see FIG. 1),computer 200 closes two-way solenoid 144 c to interrupt the flowcommunication between vacuum flow path 106 g and vacuum system 146. Asdescribed above, this causes the aerosol flow to enter depositionchamber 138.

When particle deposition system 100 is operating in bypass mode, two-waysolenoid 144 c is closed so that vacuum flow path 106 g is not in flowcommunication with vacuum system 146. During initial stabilization ofparticle deposition system 100 in bypass mode, computer 200 keepstwo-way solenoid 144 b open so that vacuum flow path 106 f is in flowcommunication with vacuum system 146. As described above, this causesthe aerosol flow to be drawn into the vacuum system via vacuum flow path106 f. Whenever particles are to be deposited into deposition chamber138 (see FIG. 1), computer 200 closes two-way solenoid 144 b tointerrupt the flow communication between vacuum flow path 106 f andvacuum system 146. As described above, this causes the aerosol flow toenter deposition chamber 138.

In one embodiment, computer 200 is programmed to display a userinterface that enables the user to control the entire depositionprocess. Through the user interface, the user can input the desiredparticle count and particle size and can monitor the particle count asthe deposition proceeds. In addition, by clicking the appropriatebutton, the user can pause or terminate the deposition process. Aftereach deposition, the user interface prompts the user to determinewhether additional depositions are to be conducted. By way of example,another deposition of the same particle size may be conducted at adifferent spot on the substrate or on a different substrate.Alternatively, the deposition may be stopped and the particle depositionsystem can be configured to deposit particles having a different size.Upon reading this specification, those skilled in the art will be ableto formulate an appropriate user interface for computer 200.

Referring now to FIG. 1, once a user has input the desired depositionparameters for a deposition in DMA mode, particle deposition system 100undergoes an initial stabilization procedure in which the systemstabilizes the flows and sets the voltage being applied to DMA 134.During the initial stabilization procedure, the aerosol flow flows invacuum system 146 via vacuum flow path 106 g. Once particle depositionsystem 100 has stabilized, computer 200 automatically closes two-waysolenoid 144 c to interrupt the flow communication between vacuum flowpath 106 g and vacuum system 146 and thereby divert the aerosol flowinto deposition chamber 138. As described above, CNC 140 counts theparticles that are deposited onto substrate 10 during the depositionprocess. When the specified number of particles (“the stop count”) hasbeen deposited onto substrate 10, computer 200 automatically openstwo-way solenoid 144 c to divert the aerosol flow back into vacuumsystem 146. If desired, a user may pause the deposition process beforethe stop count is reached to, e.g., change the stop count. In oneembodiment, this is accomplished by having the user click on a “pausedeposition” button displayed by the user interface. When a user clickson the “pause deposition” button, computer 200 opens two-way solenoid144 c to divert the aerosol flow back into vacuum system 146 so that noparticles enter deposition chamber 138 while the deposition process ispaused.

FIG. 3 is a flow chart diagram 300 that illustrates the methodoperations performed in depositing particles onto a substrate inaccordance with one embodiment of the present invention. The methodbegins in operation 302 in which a flow of gas containing particles,i.e., an aerosol flow, is provided along a flow path that bypasses adeposition chamber. In one embodiment, the flow path directs the flow ofthe gas containing the particles into a vacuum. By way of example, thismay be accomplished using a particle deposition system having theconfiguration shown in FIG. 1. As deposition chamber 138 shown in FIG. 1is in flow communication with vacuum system 146, the vacuum should beconfigured to prevent the flow of the gas containing the particles fromentering the deposition chamber without drawing any significant amountof air from the deposition chamber. As used herein, the phrase“significant amount of air” means an amount of air sufficient to causecontamination to be introduced onto a substrate in the depositionchamber. To avoid contaminating the substrate, in one embodiment, theflow to the vacuum matches or slightly exceeds the flow of the flow ofgas containing the particles. It will be apparent to those skilled inthe art that the flow path does not have to direct the flow of the gascontaining the particles into a vacuum. By way of example, the flow pathmay bypass the deposition chamber by directing the flow of the gascontaining the particles into a waste receptacle.

In operation 304, the flow path of the flow of gas containing theparticles is changed so that this flow causes particles to be depositedonto a substrate in the deposition chamber. In one embodiment, the flowof the gas containing the particles is diverted from the vacuum into thedeposition chamber by interrupting the flow communication between thevacuum and the flow of the gas containing the particles. By way ofexample, this may be accomplished by controlling a valve, e.g., asolenoid, to take the vacuum out of flow communication with the flow ofthe gas containing the particles. It will be apparent to those skilledin the art that the flow path of the gas containing the particles may bechanged using a mechanism other than a vacuum. By way of example, theflow path may be changed by controlling a suitable valve, e.g., athree-way valve, or by directing a pressurized stream of air or othersuitable gas at the flow of gas containing the particles.

In operation 306, the flow path is changed so that the flow of the gascontaining the particles bypasses the deposition chamber. This may bedone to pause a deposition process, e.g., to change the stop count or tomove the substrate into a different position for another spotdeposition, or to stop a deposition process, e.g., when the number ofparticles deposited has reached the stop count. When a vacuum is used tocontrol the flow path, the flow path may be changed by putting the flowof the gas containing the particles back into flow communication withthe vacuum. Alternatively, the flow path may be changed by controlling asuitable valve or by stopping the pressurized stream of air or othersuitable gas.

The method then proceeds to decision operation 308 in which it isdetermined whether deposition is to be continued. By way of example, thedeposition process may be continued either to finish a deposition thatwas paused or to conduct additional spot depositions at differentlocations on the same substrate. If it is determined in decisionoperation 308 that deposition is to be continued, then the methodproceeds repeats operations 304 and 306 and returns back to decisionoperation 308. Operations 304 and 306 may be repeated as many times asdesired, e.g., to make multiple spot depositions on the same substrate.Once it is determined in decision operation 308 that deposition is notto be continued, the method is done.

FIG. 4 is a flow chart diagram 400 that illustrates the methodoperations performed in depositing particles onto a substrate inaccordance with another embodiment of the present invention. The methodbegins in operation 402 in which a substrate, e.g., a semiconductorwafer, is disposed in a deposition chamber. In operation 404, particlesare deposited onto the substrate in accordance with a first set ofdeposition parameters. By way of example, the first set of depositionparameters may include a specific particle size and a specific spotlocation on the substrate for the deposition. The particles may bedeposited onto the substrate in accordance with the first set ofdeposition parameters using the method described above with reference toFIG. 3.

In operation 406, without removing the substrate from the depositionchamber, particles are deposited onto the substrate in accordance with asecond set of deposition parameters. The substrate does not have to beremoved from the deposition chamber before the second deposition becauseno unwanted particles are introduced into the deposition chamber duringthe first deposition. In contrast, in conventional particle depositionsystems, the substrate must be removed from the deposition chamber sothat unwanted particles can be purged from the deposition chamber. Inone embodiment, the second set of deposition parameters includes thesame particle size as the first set of deposition parameters and adifferent spot location on the substrate than in the first set ofdeposition parameters. In another embodiment, both the particle size andthe spot location on the substrate in the second set of depositionparameters are different from those in the first set of depositionparameters. The particles may be deposited onto the substrate inaccordance with the second set of deposition parameters using the methoddescribed above with reference to FIG. 3. Once the particles have beendeposited onto the substrate in accordance with the second set ofdeposition parameters, the method is done; however, it will be apparentto those skilled in the art that additional depositions may be conductedif desired.

FIG. 5 is a flow chart diagram 500 that illustrates the methodoperations performed in maintaining particle diameter during depositionof particles in accordance with one embodiment of the present invention.The method begins in operation 502 in which gases are flowed into adifferential mobility analyzer (DMA) having a slit for passing particlestherethrough. At least one of the gases flowing into the DMA containsparticles to be sized by the DMA. The DMA may be any suitablecommercially available DMA and operation 502 may be implemented in anysystem that contains such a DMA. In one embodiment, operation 502 isimplemented in a particle deposition system that is comparable toparticle deposition system 100 shown in FIG. 1. In operation 504, thegas flows into and out of the DMA are monitored. In the embodiment inwhich operation 502 is implemented in a particle deposition system thatis comparable to that shown in FIG. 1, the monitored gas flows includethe aerosol flow through orifice 128 before the DMA, the flow throughsheath flow controller 114, the flow through orifice 136 after the DMA,and the flow through excess flow controller 140. In one embodiment, theaerosol flow through orifice 128 and the aerosol flow through orifice136 are determined by measuring the pressure differential across therespective orifices. Alternatively, the aerosol flows into and out ofthe DMA may be monitored using mass flow controllers.

In operation 506, the voltage applied to the DMA is periodicallyadjusted so that the particle diameter passed through the slit in theDMA remains substantially constant. As described above, the voltagerequired for the DMA to pass particles having a specific size is afunction of the flows into and out of the DMA. In one embodiment, acomputer or other suitable signal processor adjusts the voltage appliedto the DMA based on the gas flows into and out of the DMA. By way ofexample, the computer can accomplish this by periodically, e.g., everyfew seconds, using an equation known to those skilled in the art tocalculate the voltage required for the DMA to pass the desired particlesize based on the current flows into and out of the DMA. The computerthen compares the calculated voltage with the voltage currently beingapplied to the DMA and makes any necessary adjustments to the voltagebeing applied to the DMA. By controlling the voltage applied to the DMAin this manner, it is ensured that the passed particle size remainssubstantially constant during the deposition process. The periodicvoltage adjustments are preferably carried out during the entire timeparticles are deposited onto the substrate. Once the deposition processstops, operation 506 is finished and the method is done.

The present invention advantageously enables particles having a constantparticle diameter to be deposited onto a substrate in a depositionchamber without introducing unwanted particles in the depositionchamber. This avoids the need to purge the deposition chamber betweendepositions. Consequently, multiple depositions can be made on asubstrate without removing the substrate from the deposition chamber. Byminimizing the handling of the substrate required for deposition, thepresent invention significantly decreases the time required to producestandards having multiple depositions thereon. It also minimizes theopportunity for contamination to be introduced onto the substrate duringthe deposition process.

In summary, the present invention provides a particle deposition system,a method for depositing particles on a substrate, and a method formaintaining particle diameter during deposition of particles on asubstrate. The invention has been described herein in terms of severalexemplary embodiments. Other embodiments of the invention will beapparent to those skilled in the art from consideration of thespecification and practice of the invention. By way of example, asdescribed above, the principles of the invention may be implementedwithout using a vacuum as shown in FIG. 1. The embodiments and preferredfeatures described above should be considered exemplary, with the scopeof the invention being defined by the appended claims and theirequivalents.

1. A method for depositing particles onto a substrate, comprising:providing a flow of a gas containing particles into a vacuum, the vacuumbeing configured to prevent the flow of the gas containing the particlesfrom entering a deposition chamber coupled in flow communication withthe vacuum without drawing any significant amount of air from thedeposition chamber; and diverting the flow of the gas containing theparticles from the vacuum to the deposition chamber to cause particlesto be deposited onto a substrate disposed in the deposition chamber. 2.The method of claim 1, wherein, after a desired amount of particles havebeen deposited onto the substrate, the method further comprises:diverting the flow of the gas containing the particles from thedeposition chamber to the vacuum.
 3. The method of claim 1, wherein theoperation of diverting the flow of the gas containing the particles fromthe vacuum to the deposition chamber includes: interrupting the flowcommunication between the vacuum and the flow of the gas containing theparticles.
 4. The method of claim 1, wherein the flow to the vacuummatches or slightly exceeds the flow of the gas containing the particlesinto the deposition chamber.
 5. A method for depositing particles onto asubstrate, comprising: providing a flow of gas containing particlesalong a flow path that bypasses a deposition chamber; and changing theflow path of the flow of the gas containing the particles so that theflow of the gas containing the particles causes particles to bedeposited onto a substrate disposed in the deposition chamber.
 6. Themethod of claim 5, wherein, after a desired amount of particles havebeen deposited onto the substrate, the method further comprises:changing the flow path of the flow of the gas containing the particlesto the flow path that bypasses the deposition chamber.
 7. A method fordepositing particles onto a substrate, comprising: disposing a substratein a deposition chamber; depositing particles onto the substrate inaccordance with a first set of deposition parameters; and withoutremoving the substrate from the deposition chamber, depositing particlesonto the substrate in accordance with a second set of depositionparameters.
 8. The method of claim 7, wherein the first set ofdeposition parameters includes a first particle size and a first spotlocation for the deposition and the second set of deposition parametersincludes the first particle size and a second spot location for thedeposition.
 9. The method of claim 7, wherein the first set ofdeposition parameters includes a first particle size and a first spotlocation for the deposition and the second set of deposition parametersincludes a second particle size and a second spot location for thedeposition.
 10. A method for maintaining particle diameter duringdeposition of particles onto a substrate, comprising: flowing gases intoa differential mobility analyzer having a slit for passing particlestherethrough, at least one of the gases flowing into the differentialmobility analyzer containing particles; monitoring the gas flows intoand out of the differential mobility analyzer; and periodicallyadjusting a voltage applied to the differential mobility analyzer sothat a particle diameter passed through the slit remains substantiallyconstant.
 11. The method of claim 10, wherein the operation ofmonitoring the gas flows into and out of the differential mobilityanalyzer includes: measuring a pressure differential across an orificelocated before the differential mobility analyzer; and measuring apressure differential across an orifice located after the differentialmobility analyzer.